Fractionation of oils



Feb. 25, 1941. G. l.. PARKHURsT FRACTIONKTION OF OILS Filed Feb.' 25, 1952 patented Feb. 25, 1941 UNITED STATES 2,232,122 y raAcrroNArroN or ons George L. Parkhursa Chicago, lll., assignor to Standard Oil Company, Chicago, Ill., a corpora` tion of Indiana Application February 25, 1932', Serial N o. 595,014

21 Claims.

This invention relates to the fractionation of wax-bearing oils, and particularly. wax-bearing mineral oils, into' one or more wax fractions and one or more oil fractions by the use of special solvents. i

One objectof this invention is to provide a more eliicient method for dewaxing mineral oils by the use of special solvents. Another object is to provide a dewaxing process in which the solvent loss can be minimized. vA further object is to provide such a dewaxing process in which a portion of the filtrate is separated from the remainder-thereof and recycled to the beginning of the dewaxing process. Ak still further object is to provide a dewaxing process using special solvents, in which the dewaxed solution is separated into two or more liquid fractions containing lubricating oils differing in quality. Another object is to provide a process of the type last mentioned in which one of the liquid fractions is recycled to the beginning of the dewaxingprocess.

Another object is to provide a process to accomplish the aforementioned ends with high thermal eiliciency. Y

Further objects will become apparent as the description proceeds. My invention may be more readily comprehended by reference to the accompanying drawing which represents a conventionalized flow diagram of the process.

Referring now more particularly to the drawing, I represents a suitable storage receptacle for the solvent or solvent mixture used in the process. As to the selection of a suitablesolvent or solvent mixturefmore will be said hereafter. Another storage receptacle 2 provided for the wax bearing mineral oil which is the stock on which the process of my invention operates. Since in many cases this wax bearing mineral oil will be very viscous, or even solid, it is generally advisable to provide heating means f or storage'receptacle 2. In the diagram this is accomplished by means of steam coils 3. In operating the process solvent is removed, preferably continuously, from receptacle I through line 4 by means of pump 5 into mixer 6. Simultaneously the wax-bearing oil is removed from receptacle 2 by means of pump 1 and introduced into mixer 6. Mixer 6 may be of any type adapted to effect complete solution of the wax-bearing oil in the solvent. For instance. it may be of the well-known orice type. In some cases itmay be desirable to add heat prior to or during the mixing operation vin order to eiect complete solution. In the diagranlgshown, this is done by means of a steam jacket surround.-

that other means can be used when it is necessary to supply heat. It is desirable that solution be effected at the lowest possible temperature so as to minimize 'the chilling which is necessary in the next step of the process. The dissolved Ioil passes out of mixer 6 and through a preliminary chiller 8, which is preferably cooled byr means of cold water. This chiller may be of anytype, for

ture of the solution is lowered by'heatexchange Y with still another intermediate product of the process. 'Facilities' are also provided forby-passing chiller I3 by' closing valve I2; and .opening valv'e I 4. VBy means of 'or asimilar series of chillers the temperature of1`1 :ljxe4 solution of wax-bearing" oil is lowered toth'e temperature desired forV the removal of wax. Inother words, the plant is so constructed that vthe major portions of the wax will be precipitated at the temperature produced bythe iinalchiller. More will be said hereafter as to the degree of chilling required. 'I'he solution from the lastchiller mll generally needI to have its pressure raised in order to force it through the wax removing 'equipment. This is done by means of pumpV I inthe case of the process illustrated by the drawing., The solution is then passed through lterfIE-` where the -precipltated wax is removed. This'lter may be of any desired type. For instance, it may be a continuous rotary' lter or it may be abattery of plate and frame presses arranged vvsoi that continuous operation can be Amaintained by using a portion of the presses while the remainder are being cleaned. Although my process -is devised more particularly for yconditionswhere wax will be precipitated in substantiallycrystalline form, it may nevertheless be desirable in some cases to replace filter I6 by some other type:V of wax`removing equipment, such as a centrifuge or set` tling tank and it is to be understood that the use of such equivalents in place of lter I6 is within the scope of my invention. Suitable provision, not shown, may be vmade for washing the lter cake, etc. The separated wax is removed through line Il, which may suitably be a heated pipe or n ing mixer 6, but it will "eaflilybecomprehended a screw conveyor. into a storage receptacle Il,

from which the wax can be removed for further treatment or use as desired. 'I'he filtrate from filter i6 is then further chilled, ilrstv passing through pump I9 and thenin series through chillers 20 and 2|. Part of this additional chilling may be done by means of heat exchange with one ofthe intermediate products of the process, but for the iinal chilling it will generally be necessary to use external refrigeration, such as can be pro- 10 vided by cold brine or direct ammonia expansion. 'I'he iinal chiller is adapted to lower the temperature of the solution to a point at which it will become separated into two liquid phases. 'I'he old solutions from the iinal chilling operation pass through line 22A and valve 23 into settler 24-wherein the two liquid phases are allowed to settle and are separately removed. Settler 24 may be. of any conventional type. The one diagrammatically shown is a simple continuous' gravity settler, the mixed liquids formed by the chilling being introduced into the settler at an intermediate point; the two phases separating underthe force of gravity, the lighter one being continuously removed from a point near the top 25 through valve 25 Iand line 26 into a storage receptacle 21, while the heavier phase is removed from a point near the bottom through line 28 and valve 29 into-storage receptacle 30. The rate of removal of these materials from settler 24 is 30 such as to balance the rateat which they are introduced into the settler through valve 23. It is to be understood that other types of continuous settling equipment may suitably be used or that settlerI 24 may be replaced by a` battery of batch settlers. ,Y

fAn inspection of the process as thus far described reveals tht it consists 'in dissolving a wax-bearing oil, preferably a wax bearing min-N eral oil, in a selected solvent or solvent mixture,

* 49 the chilling of the solution thus formed to a delv-Y waxing temperature, the removal of .the wax, the further chilling oi' `the dewaxed solution to a pelin-t at whichtwo liquid phases separate in predetermined proportions and the separate removal of these two liquid phases. The purpose oi the' dewaxing step is well known. .'I'he advantage of combining it with 4the solvent fractionation of the lubricating oil constitutes one of the maior discoveries included within -the 'scopeo'f the/pres- 50 ent invention., It has been found that when an oil is dlssdlved in a suitable selective solvent or solvent mixture and chilled to a point at which two liquid phases are formed thatl one of these phases will contain a relatively large proportion .55 of the solvent and .a relatively small proportion of the oil, whereas the other phasewill contain a relatively small proportion of solvent and arelatively large proportion of oil. It will be found, moreover, that there is a great difference in the 50' chemical nature. as well asin the physical proper;

ties of the oils contained in the' respective liquid phases. Thus, for example, when the process is operated on a wax bearing mineral oil of the i mixeddbase type, it will be found tlrat the phase containing the greater proportion o1.' solvent will in general contain a mineral oil of relatively naphthenic characteristics, whereas the phase containing the lsmaller proportion of solvent will contain an oil of a considerably more parafilnic v nature. This latter oil will, of course, .be much l more valuable for ordinary lubricating purposes than the former. lFor instance, it will have a much lower temperature co-efllcient of viscosity and a much greater resistance to oxidation and sludging. In other words, by means of my procl portion, oi' an oil which is `inferior for ordinary 124 into receptacle 21, while the phase containing the larger proportion of solvent, together with the 10 dissolved naphthenic oil, is removed from the bottom oi' settler 24 into receptacle 3l. It will be understood that the speciilc of the solvent or solvent mixture selected will generally have a controlling influence upon 'which of these two .15 liquid phases is the lighterV and it will further be understood that in some cases the phase containing the naphthenic oil will be the lighter and will therefore be removed from the top ot the settler while'fthat containing the paraiilnic oil will be 20 removed trom the bottom thereof. In any event, it is possible by means of my process, to separate the dewaxed -oil solution by chilling it to a selected temperaturev into one liquid pbase containing the .more desirable portions or the ou, together, 25 with a relatively small proportion of the solventand another liquid phase containing the bulk of the solvent and, in general, a relatively small pro' monoamine purposes. 30

In the vilow diagram of the process. the separated paramnlc oil. having characteristics superior to those of the original dewaxed oil, passes out of receptacle 2'l, -through valve 3|, pump l2 and valve u to chmer u where its capacity to absorb 35 heat is utilized to lower the temperature of the incoming solution. In some cases it will be understood that the paraillmc oil containing some' souvent may bei sumciently viscous at the low temperatures involved to make it impractical to ,40

utilize its capacity to absorb heat and in this event chlller 4Il may be by-passed by closing valve I3 and opening valve 34. When this is done it will generally be desirable to remove chiller Il andrshunt Vtheincoming solution around it by 45 closing valve 0 and opening valve lil, as hereinbeiore described. In either mode of operation the paraillnic oil, containing some dissolved solvent, will pass through'line 35 into still I6, which is shown as a pipe heater. The solution is heated 50 in this still to aiemperature adapted to the eilicient operation oi bubble tower 38. This temperature will depend on the nature of the solvent and oil, the concentration of the oil and other iactors.- ySteam should, in most cases, be injected .55 into still n, t-lirbugh line 31 and/or, into the ,base

of bubble tower it in order to eifect distillation without injury to the .parailinic oil. The vapors from still 3i pass Athrough line 39 and enter hublble tower Il at an intermediate level therein. w Bubble tower 3l is adapted tothe removal of the solvent or solvent mixture, which in general has a relatively low boiling point, from the oil; 'Ihe oil will pass out of the base of bubble tower Il. thmugnvaive n, into a suitable storage reeep- 55 tacle Ill .from which it may be removed through valve 42, as desired, for-further treatment or use.

In some cases it may be possible to use the ,paraiilnic' oil ironi storage receptacle ll directly as an improved lubricant, but in other cases it will be 70 desirable tov give it further treatments, as for instance, with sulphuric acid and/or Iullers earth. The solvent varpors from bubble tower 38 ordi narrlly pass out through line 44l and valve 44 (valve being closed) Ainto condenser where 75 from separator 41 through valve 46 and is returned to receptacle I through line 56. If the 4solvent being recovered is heavier than water, it will, of course, be drawn off at .the lower level and the water at the upper level. Furthermore, it is to be understood that this wholearrange` ment f still, bubble tower, condenser and separator is merely for the purpose ofseparating the parailinic oil separated in settler 24 from the relatively small amount of solvent which is necessarily carried with it. This equipment can conveniently be replaced by any other suitablev type of separating equipment. -For instance, the solvent may be stripped from the oil bymeans of a vacuum still. In many cases it will be desirable to so arrange the distillation equipment that it will be unnecessary to vaporize -the oil.

Returning now to the other intermediate product removed from settler 24, it will be recalled that this constitutes the bulk of the solvent carrying `in solution therein certain naphthenic portions of the original lubricating oil. This second liquid phase is shown as being removed from settler '24 through line 26 and valve 29 into storage receptacle 30. From-storage receptacle 30 this material may optionally be passed throughone or more of three alternative series of operations. These three series of operations may be succin'ctly described as (l) recycling to the dewaxing operation, (2) separate recovery .of the solvent and nalphthenlc oil, and (3) further chilling to form two further liquid phases.

These various alternative procedures will be discussed in the order named, together with their concomitant advantages. In the first procedure, the solution from receptacle 30 is removed therefrom through valve 5I by means of pump 52 and thence through valve 53, ultimately passing into mixer 6, through line 54. It will be readily ccmprehended that this constitutesfrecycling the so-- lution contained in receptacle 30 back to the beginning of the process and it will furthermore be readily seen that this could alternatively be done by leading line 54 into receptacle I or receptacle 2 or by introducing it into chiller I0 or by introducing it at some other point in the processprior to the removal of wax by means of filter I6. In any of these procedures it will'be seen that complete utilization of the capacity of the solution from receptacle 3l to absorb low temperature heat will be had.- This makes for a very high degree of thermal efliciency, since the solution in receptacle 30 `will generally constitute by far the larger proportion of the total filtrate from filter I6 and since it will pass, at a very low temperature, directly into the material to be dewaxed, thereby cooling it very materially and eiiiciently. In many cases this will allow chillers 6, I6 and I3, or part of them, to be dispensed with and thereby greatly increase the thermal eiciency of the process. It will be understood, of course, that ifline 54 is led into mixer 6 it would be thermally ineiiicient to heat the said y mixer 6 and that in case it is necessary to introprocess, fo.` instance, vjust prior to introduction of the solution into filter I6.`

In addition to the high thermal emciency ob tained by operating this process in this manner there is another very, prominent advantage. in

that solvent losses are kept at an unusually low iigure. .In operating dewaxing processes using .special solvents, the largest item of expense has,

in the past,` resulted from the loss of considerable volumes of solvent during the operation of the process. 'I'he special solvents used are, without exception, relatively expensive and these losses represent a very important economic consideration. In the operation vof a conventional dewaxing process' using special solvents, the solvent is recovered from both the wax and the oil by means of distillation and since it is diiiicult,

if not completely impossible, to arrange distillation equipment in such manner as to obviate all solvent losses, a large proportion of the total y solvent loss occurs in the distillation step. It will be observed that operating my process in the manner described the great majority of the total solvent passes into storage receptacle 30 and is removed therefrom and recycled back to the dewaxing operation in the liquid phase. Thus the great bulk of the solvent circulated in the process is never vaporized and solvent losses are thereby maintained at an exceedingly low ligure. Furthermore, it has been found that in some cases the recycling of the more naphthenic portions of the oil has a desirable eect on the dewaxing operation which may possibly be explainable as a favorable inuenceexercised upon the crystallization of the wax tending to promotea type of wax crystallization more consonant with eflicient wax removal than that otherwise prevailing.

lComing now to the second alternative procedure which can be applied to the solution in receptacle 30, it will be recalled that this, in brief, consists of separating the naphthenic oil from the solvent and separately recovering it. In Aorder to accomplish this the solution is removed from receptacle 30, through valve 5I, pump 52 and line 55 (valves 53, 56, and 51 being, in general, closed). By closing valve 58 and-opening valve 59 this solution may thenvbe passed through chiller 20 where its capacity to absorb low temperature heat is utilized in'lowering the temperature of the solution passing from the dewaxing operation. Under different conditions of operation it may be desirable to utilize this capacity to absorb low temperature heat, in whole or in part, prior to, rather than subsequent to the f Y 68 and into still 6I which may be similar to still 36. The heated stream from still 6I passes out therefrom through line 62 and into an intermediate sectionof bubble tower 63, the naphthenlc oil being removed from the base of bubble tower 63 through valve 64, into storage receptacle 65 i from which it can then be withdrawn through valve 66 for anypurpose to which it is desired.

to put it. The solvent vapors from bubble tower il will commonly pass out therefrom through valve 6 4 (valves 65 and 66' being closed) and thence through line 61 into condenser 46 where it joinsthe solvent vapors from bubble tower 38,

being condensed together with them and returned tol storage receptacle I or to some other point in the process, preferably prior to mixer 6. It will be seen that by operating this process in the manner last aforementioned the original waxbearing oil is first dewaxed at a selected tempervature and then echilled to a temperature at which the solution separates into two liquid phases, one of them containing a relatively par-V amnic oil and one of them a relatively naphthenic oil. each oil being separately recovered as a product of the process andthe separated solvent being recycled to the beginning of the process.

This procedure constitutes, under many cir# cumstances, one of the most desirable modes of operating the process`of my invention since it allows eillcient removal of wax-which is commonly necessary in order to produce hih quality oils yfrom wax-bearing stocks.- and then, without removal of the solvent from the dewaed oil and without loss of the low temperature of the solu-4 tion containing the dewaxed oil, proceeds by further steps to separate the oil into two fractions, one .of them of highly improved characteristics for ordinary lubricating ma and the other of them, although not highly suitable for use as an ordinary lubricant, g interesting potentialities as a by-product.

Another advantage of this type ofv operation lies in the fact that the oil which'is sublected to the solvent fractionation 1s a wholly, or at least partially, dewaxed oil and this fact lends itself to emcient separation I,of the oil into two liquid phases, since the presence of excess wax during the solvent fractionation step tends to interfere therewith by rendering one vof the separated phases semi-solid or slushy.

Two procedures to which the solution in storage receptacle Il maybe subjected have been deb scribed; namely, recycling the solution to the dewaxing operation and recovery of its components (solvent and naphthenic oil) separately. It will'be understood, however, that my invention contemplates, and in many cases it will be desir-y able, to use both of these procedures simultaneously. That is, by opening valve 53 as well as valve 5i and/or valve 59, a portion of the solution from receptacle Il may be recycled and another portion passed through chiller Il and/or chiller 2l and,then separated into its components. This typeof `operation will allow to a considerable extent a combination of the Aad vantages of each of the two types of operation .when separately used. Thus a considerable por- .non or the total solvent wm be recycled without being distilled, thereby reducing solvent losses scribed. y

and accomplishing a large amount of chilling by direct heat exchange, while another portion of the solution is separatedl into its components, a portion of the more naphthenic oil being continuously removed from the system, which tends to increase the quality of the paraillnic oil produced bythe process and at the same time yields a useful by-product in the'formi of the na'phthenic fraction itself.

Before discussing the third alternative procedure which may be applied to the solutionin receptacle 3B it will be desirable to discuss some of the features of the process as thus far de- As to the selection of a suitable solvent or solvent mixture for use in my process, it will be readily comprehended that in general the most satisfactory solvent will be composed of a single component, since by using a single component solventfewer difflcultiesmre encountered in the removal of the solvent from the oil and in recycling it. Furthermore, another important advantage of using a single component solvent is that the solvent carried by the paraillnic oil and by the naphthenic oil will De the same and it will therefore be unnecessary to provide for returningV the solvent from these two sources to the beginning of the process at the same rate. Another advantage is that difiiculties due to the separation of a portion of the solvent as a separate liquid or solid phase during the chilling .operation are more rarely met with. Nevertheless'it will be comprehended that 1n some cases suitable solvents comprising two or more components may be used as hereinafter described.

Since one of the .unique features of my process is that the oil is wholly. or to a major degree, dewaxed prior to its fractionatiominto two ,liquid phases, it will be understood that it will be desirable in many casesto, select the solvent used in thev process according to its properties as a dewaxing agent. It is known that in order to remove wax by the use oiv special solvents at any given temperature as completely as possible it is necessary to use a solvent oi such nature and in such' amount that a portion of the oil will be on the verge of precipitation therefrom at the dewaxing temperature since when the oil is barely soluble the wax will have themaximum insolubility. Furthermore, it is known that in order to remove wax completely from typicalwax-bearing lubricating oil fractions it is necessary-that this dewaxing operation take placeat a fairly low temperature, say minus 10 l". or below.

Consideration of these principles Qleads to theY conclusion that for many types of operation the most satisfactory solvent or solvent mixture for use in my process is one which is adapted to I remove the wax as completely as possible at a selected dewaxing temperature. Such a solvent not only produces final oils which. are wholly or substantially wax free, but it removes the wax as emciently as possible at the selected temperature. Furthermore, since -this emcient removal of the wax carries with it as an inevitable concomitant, the condition that the'oil be on the verge of precipitation, it will be apparent that the dewaxed oil solution may be separated into two liquid phases with the minimum amount of additional chilling, since any chilling substantially below the dewaxing temperature will tend to throw a portion of the oil out of solution or, in other words, it will cause the oil to separate into two liquid phases, one of them vcontaining an oil of a relatively lparafnnic nature and the other y an oil of a relatively naphthenic nature.

A considerable number of solvents and a much larger number of-solvent Vmixtures lare capable of accomplishing this purpose and their selection is. for the most part, a simple matter of experiment in accordance with the principles laid down in this disclosure. Among the solvents which l by chilling thesolution thus formed to a temperature in the neighborhood of minus 10 F. or minus 15 F. A further chilling to a temperature of from 15 F. to 60 F. lower than the dewaxing temperature will serve'to separate the dewaxed oil solution into suitable proportions of two 1iauid phases. The'exacttemperature chosen for this latter operation will depend upon the respective quantities of the two liquid phases desiredv and more particularly upon a balancebetween ditional chilling and the cost -of the additional refrigeration. Other factors may also affect the decision as to the desired temperature of the nal such as, for instance, the viscosity and resultant ease of separation of the two liquid phases formed. These considerations, however, are mere lmatters of conventional vengineering practice and will not be considered in detail-here.

As a specific example of a process of thisgeneral type a wax bearing lubricating .oil fraction produced by the fractional distillation of a typical Mid-Continent crude, said lubricating oil fractionhaving a viscosity at 210 F. ofapproximately '75 seconds Saybolt, may be dissolved continuously at'slightly elevated temperatures in two and one-half times its Aown volume of isopropyl ether and the solution thus formed may be chilled to V a temperature of minus 10P F.l The wax contained in the'wax-bearing mineral oil will be substantially completely precipitated at this temperature and may be removed by suitable means, as for instance, by lter pressing. The dewaxed oil solution from this operation may then be additionally chilled 'to a temperature of v minus 45 F., at which temperature. the solution will separate into two liquid phases, one of which will contain the bulk of the oil anda relatively smalrproportion of the isopropyl ether and the other of which will contain, in most cases, a

.smaller proportion of the oil and a larger proportion of the isopropyl ether. Furthermore, it will be found that the oil which was thrown out of solution (i. e. the oil containing the smaller proportion of' isopropyl ether) have diiferent properf ties and will be more parafnic than that retained in solution in the bulk of the isopropyl ether.

These tw'o liquid phases may be continuously separated from each other in a continuous settler or in a battery of batch settlers and it is generally desirable to utilize their capacity to absorb low temperature heat by passing them through Achillers or heat exchangers whereby their temperature -is raised and the temperature of the incoming solution lowered. Thereafter the two oil fractions may be separated from the isopropyl ether carried therewith by means Iof sui-table distillation equipment and the two oil fractions may removed t3 storage prior to further treatment or use. The separated isopropyl. ether is conveniently recycled -to the beginning of the Process. As an alternative, the whole or a portion of the isopropyl ether containing'dissolved naphthenic oil may be directly recycled to the beginning of the process, thereby securing the advantages in heat exchange and low solvent Vloss which have previously been described.

Although the vadvantages of operating in such manner and at such temperature as to remove substantially all the wax prior to the separation -advantage of this method of operation is the lower refrigeration requirement. In some instances, no refrigeration at all beyond ordinary cooling water .temperature is necessary. Furthermore, by operating at higher temperatures the viscosities of the solutions are higher and therefore pumping costs are lower and less diiiiculty is encountered in the separation of the various phases produced. The principal disadvantage'of working with these higherl temperatures isl that the incomplete removal of wax sometimes introduces complications in the later cooling stages.

As an example of such a process operating at a higher temperature, nitxobenzene may be used as a solvent in dewaxing a lubricating oil of the general type discussed above, the solution being effected at an elevated temperature, say F., the dewaxing taking place after chilling to about 5U-'70 F. and the, separation of the two liquid phases taking place at a. temperature of approximately 20-40" F. Another suitable solvent is pyridine. In its use dewaxing can conveniently be accomplished at l0-50 F. andthe separation into two liquid phases can -be accomplished at Although certain specic' solvents have been described for use inmy process it will be understood that a great many organic liquids which vare solvents for the oils'and waxes in question may be used'with greater or less efficiency if the conditions of operation are properly selected. Petroleumfractions or wholly hydrocarbon solvents are-generally unsuitable. Amongst solvents which are suitable for use alone or in mixture in my process when operating on various types of oils may be mentioned methylethyl ketone,I dichlorethyl ether, isopropyl alcohol, butyl alcohol, acetone aniline, phenyl acetate, benzaldehyde, propionic acid, etc. It is .to be understood, however, that with any speciiied oil some of these solvents will not work eiiiciently due -to the solubility of the oil and/or wax being higher or `lower lthan Such processes may be advantageous under some circumstances. Furthermore, it is to be understood that if the wax is only incompletely removed prior to separation of the oil into two fractions, it will generally occur that the remainder of the Wax, or most of it,.will be thrown out of solution together with the Ylnore parailinic oil during the liquid frac- Vmay be separately removed after chilling to a somewhat lower temperature.v

tionation step of the process and this wax can f be removed by desired. Although in the process as thus far described it has been assumed that the composition of the solvent did not vary throughoutv the different stages of'the process, it will b readily seen that suitable subsequent operations if it is possible, and may, under certain conditions,

V-be desirable, to modify the composition and/or change the amount of .thesolvent or solvent mixture between the' dewaxing step and the subsequent fractionation of the oil. In the diagram this possibility is shown by means of a supplemental solvent receptacle 468 'from which, by means of valve 69 and pump I9, an .additional i amountrof .the solution contained in receptacle i or of a diiferent solvent may be introduced into the solution flowing from the dewaxing filter llito chiller 20 or at some other point between iilter -IG- and settler 24. If the solvent added at this 6' point is of the same composition as that pensed with'and solvent may be supplied at this lcon-v tained inreceptaclevl, receptacle can be dis- `poilnt directly from receptacle I or alternatively,

a. portion of the solvent flowing from separator' Il to receptacle I may be diverted to receptacle .Il xby means of a suitable line not shown.'

This introduction of an additional amount' of solvent may be desirable in some cases to reduce the viscosity of the solution being separated in settler 24 in order to enhance the settling opera tiop. In other cases, however, it will be found more desirable to add an additional solvent sub-1 Vphases will, in general, be of diii'erent compositimately passing in vapor form into gb tion but that, in general. both of these solutions will contain some of the solvent introduced from receptacle I'and some of the solvent introduced from receptacle l. Means are therefore provided for returning to each of these two receptacles a solvent or solvent mixture of substantially the same composition as that withdrawn therefrom in order to maintain the processen a constant basis. In order to accomplish this the solution withdrawn from receptacle 21 and uie tower 3l may be separated into three fractions rather than two. Specifically, the paramn'ic oil may be removed from the base of bubble tower I8, through valve Il, into storage receptacle ll as heretofore shown and the solvent vapors may be 'fractionated into two components, the lighter of them being withdrawn from the top of' the hubble tower through line 4I and the heavier of them being withdrawn from an intermediate point in the bubble tower Il through pump 1l. Suitable auxiliary fractionation means, such as reilux equipment, or dephlegmators', may of course be provided, If the vapors removed through line I they will'be'passed as heretofore described through valve u. condenser II. separator Il,

.valvellandlinellbacktoreceptacle Iandthe liquid withdrawn from bubble tower 3l from an intermediate point therein by means of pump Il willpassthroughvalve 1I.(valves12andllbe ing closed), line 12a, condenser Il (if necessary).

. spondingly. the material withdrawn from bubble tower through pump 'Il may be that which itisdesiredtoreturntoreceptaelelratherthan' to receptacle Il. In orderl to accomplish this end, material from line 43 is passed through valve 4I (valves Il and il being closed) and line 'IIa into condenser 'Il and separator il and thence through valvev 'II back to receptacle il. Simultaneously the heavier solvent fraction is correspond to the liquid. material in receptacle withdrawn from bubble tower AIl by meansl of pump Il and passed through valve l1, condenser II, separator l1, valve 4l, and line Il back to receptacle I. It will thus be seen that by appropriate manipulations f valves M, ll and 12- either the lighter or heavier solvent fraction can be returned to receptacle I and the other fraction to receptacle Il.

Similarly, in the case where the solvent or solvent 'mixture in receptacle (l is'diiferent from the solvent or solvent mixture in receptacle I, it 'will generally be necessary, in recovering the solvent from the solution in receptacle Il, to separate it into two fractions. returning one of them to receptacle 68 and the other to receptacle I. This can be done by means of distillation equipment similar to that described in the last paragraph as being applied to the solution contained in receptacle 21. In detail. this can be accomplished by passing the solution from receptacle 3l outthereof through valve il. pump i2, and line II, thence through valve l and/or valve Il through chiller Il and/or chiller 2l into line Il,

kstill II, line i2 and bubble tower Il. Bubble tower Il is arranged on the same general principle as bubble tower Il. In other words, the lighter solvent vapors pass out from the top of the tower and the heavier solvent fractions are drawn out from a lower portion or tray of the tower. If the lighter solvent fraction is the one which it is desired to return to receptacle I it will be passed out of bubble tower 63, through valve Il (valves and Il being closed) into line I'I 4and thence through condenser separator 41, valve ll and lin'e Il back to receptacle I. l 8imultaneously, the heavier solvent fraction would be drawn oi! throughpump Il and valve 1I passing through-condenser 'I3 and separator I4 (condensed steam being drawn oi! through valve 18) and'out therefrom through valve Il back to receptacle Il. However, as previously described, in the case of the solvent contained in receptacle 21, it will sometimes be desired toreturn the heavier solvent fraction to receptacle I and the lighter fraction .to receptacle Il instead of vice v'ersa. In this case valves Il and will be lopened and valves Il and'll will be closed. It

will be noted that this will accomplish the passage of the heavier' fraction into the line formerly carrying the lighter one and the lighter fraction into the line formerly carrying -the heavier One.

Bubble towers I. and Il. or other suitable fractionating equipment, may be designed in accordance with well known principles in such manner as to effect the return 'into receptacles I and Ill respectively of solvents or solvent mixtures having the DNDer composition necessary for the operation of the process. Other suitable types of fractionating equipment may be employed:

It will furthermore be readily comprehended, although means therefore are not speciilcally shown in the drawing. that the composition of the solvent or'solvent paling from the dewaxing step'of the to theoil fractionation step mayl be modiiled, not only'by the addition of more of the' same or a fdlderent solvent, but also by the removal 'of a portion of the solvent. 'Rius'.'forinstanca it irpossible. by re- 70 reuse.

It will generally be found more desirable, however, to modify the composition of the solution, if at all, by the addition oi' extra material from receptacle 68, as previously described, rather than by removal of a portion of the solvent. As has previously been suggested, the composition of the solvent lor solvent mixture in receptacle 68 may be identical with that in receptacle l. In this case considerablesimpliiication in the solvent recovery system may be effected However. about the only purpose which is served by adding an additional. quantity of the same material subsequent to the dewaxing operation would be to dilute` the -solution and thereby to lower its viscosity in order to enhance separation of the two liquid phases subsequently formed. In many cases it is more desirable to add a dierent solvent or solvent mixture subsequent to the dewaxing operation rather than the one initially used. Furthermore, it will be found most generally desirable that the solvent or solvent mixture added be one having a lower solvent power for oil than does the one initially used. This will enhance separation of the solution into two liquld'phases or, in other words, will decrease the solubility of the more paraiiinicv oil in the solution. The net effect ,of this is that a more complete separation into two liquid phases may be had at any given temperature or the same separation can be effectedwith less'refrigeration. In some instances if a large amount of al material having poor solvent power for the oil is added, it is possible to effect eiiicient fractionation into two liquid phases without any additional chilling whatever.

lAs an example of an operation of my process using two separate solvents, a wax-bearinglubricating oil fraction of the type previously described may be continuously dissolved at ordinary or slightly lelevated temperatures in two. and a half times its ownvolume of isopropyl ether.

The temperature may be lowered by suitable heat exchange means similar to those which have been described, to a temperature somewhat below zero degrees Fahrenheit, whereupon the great preponderance of the total wax content vwill be precipitated and may be removed by means of a filter press. Subsequent to this dewaxing, acetone may be added in proportion equivalent to one-half the volume of the original oil. This '50 acetone should preferably be added cold, thus assisting in reducing the temperature of the modified solution to a point in the neighborhood of minus 25 to minus 40 F., whereupon the more paraiinic oil is precipitated, together with some portion of the solvents. A more complete precipitation is obtained in this way than when isopropyl ether is used alone without the addition of acetone. A portion of each of the two solvents used will be found in eachof the two liquid phases formed at the low temperature mentioned and they can be separately recovered in distillation equipment similar to that which has previously been described. It will be found in this case that the vapors passing oi! from the top of the bubble tower will be rich in acetone land should be returnedto receptacle 68 while those passing off from the intermediate point in the vbubble tower will have relatively little acetone in them and should be returned to receptacle I for However, it is usually diillcult, or impossible, to completely separate the two solvents and when the processreaches equilibrium the solvent contained in receptacle I will contain some acetone and thatcontained in receptacle 68 will contain some isopropyl ether. This, however, does from' the other.

in accordance with this third alternative pro.

not introduce any material diiliculties or vitiate the operation but should be 4taken into account in selecting the desired dewaxing and oil fractionation temperatures, etc.

Considerable has been said relative to therecovery of solvent from receptacle 30. It will be understood, however, that in one of the alternative methods of operating my process the material contained in receptacle 30 is recycled -back to the beginning of the process without recovery of the solvent and in this case it will, of course,

, be unnecessary tol use the second solvent recovery system at all.

Returning now to the discussion of the aforementioned third alternative method of operating my process, it will be recalled that this consists in rechilling the `solution contained in receptacle 30 to a still lower temperature to effect its separation into two additional liquid phases. Referring again to the drawing, the solution in receptacle 30 may be withdrawn therefrom through valve 19 by means of pump 80 into chiller 8| where its temperature is lowered by contact with .l a suitable refrigerating medium and thence into settler 82, which may be of any of the types described in the case of settler 24. Two liquid phases will be separated in settler 82, the relative volumes of each of them will be dependent upon the temperature to which the solution is chilled and said temperature should be selected to achieve the results which are desired in any given case. The lighter fraction formed will be continuously drawn off from settler 82, through valve 83, into receptacle 84 while the heavier fraction will be drawn A0E continuously through valve 85 into receptacle 86.

It will be found that the fractionin receptacle l.

86 is, in general, composed of the more paramnic fractions of the generally naphthenic oil contained in receptacle 30, together with a portion in receptacle 86 will, of course, be more naphthenic than that contained in receptacle 21, but it will be more paraillnic than the fraction drawn off into receptacle 86. In other words, the oil phases thus formed may be withdrawn from the vsystem for further treatment or use through valve 81 and/or valve 88 respectively. Furthermore, either of them may be recycled back to the beginning-of the process, thus the intermediate oil carrying .some solvent may be withdrawn from receptable 84, through line '89 and valve 90 (valve 56 being closed) by means of pump 8| and thence back to a point at or near the beginning of the process. y contained in receptacle 86 can be withdrawn therefrom through valve 92 (valve 51 being closed) by means of pump 93 into line 54 and thus recycled. When it is chosen to recycle one of vthese two fractions it will,- in general, be desirable to recover the solvent and oil separately Since, in operating my process cedure, it will not generally be desired to recover separately any of the naphthenic oil contained Similarly, the material Y 40 of the solvent. The oil contained in the solution in receptacle Il. it will be possible to utilize the recovery system. formerly appliedttp the material in receptacle Il for the recovery of oil and solvent from the material containedin receptacle Il or that contained in receptacle It. If it is desired to recover the solvent and intermediate oil from the material in receptacle Il, it will be passed out therefrom through line I9, valve I6 (valvesil and Il being closed), pump |42. line 55 (valve il being closed) valve Il and/or valve il, chiller l! and/or chiller 2l, line Il, still il, etc., the solvent ultimately returning to receptacle I and/or receptacle Il` and the intermediate oil passing into receptacle 65.-

Similarly, if it is desired to recover the highly naphthenic oil and solvent from receptacle l6,-

, this. may be done by closing valves Si and 92 and withdrawing the material from receptacle 86 through valve 51, pump i2, line 5l, etc., the solvent being ultimately returned to receptacle I and/or receptacle i8 and the very naphthenic oil being collected in receptacle $5. It will be understood that in some cases it will be desired separately to recover oil and solvent in the case of both the material in receptacle and the material inreceptacle II. In this case a sepa"` rate solvent recovery system similar'tothe two previously 'described must be installed.

It will also be understood that it is possible to modify the composition of the solution passing out of receptacle Il prior to its further chilling or separation into two liquid phases and this .can be done by introducing more of the same or a diiferent solvent through valve ll from receptacle 95. This will generally necessitate further complications in the solvent recovery system which are not shown but which may readily be worked out -in accordance withthe general principles previously discussed.

When operating my process in accordance `with this third alternative procedure the choice of the exact method used will depend upon the individual circumstances and the results which it is desire to obtain. Very often it will be desirable to recover the intermediate oil in receptacle Il and to recycle the material in receptacle 88. This, as will be apparent, will re- -sult,'looking at the process as a whole, in the recovery of two oil fractions, one a highly paramnic vfraction and the other an intermediatefraction.

The most naphthenic portions of the oil would be recycled together withthe bulk of the solvent. thereby accomplishing eillclent heat exchange and low solvent l. However, this. mode of procedure would not result in the removal of any of the most naphthenic portions of the oil and this would in turn work to the detriment of the quality of .the fractions which are recovered since, the highly naphthenic fraction not being removed, would have to -pass ultimately into the material recovered in receptacle I I. There. fore it may sometimes be desirable to separately recover the very naphthenic oil from receptacle it and to recycle the intermediatejfraction from receptacle Il, thus removing from the process a highly paraillnic oil and a highly naphthenic oil, continuously recycling'the intermediate portion, and thereby accomplishing a greater ultimate separation into parailinic' and naphthenic DOrtions..

It is to be understood'that the words paraiiinic and naphthenic as used in the `specication and claims are relative terms/fand are not intended to imply that other types'it con,

stitucnts are absent. .The term paraiiinic" is mtely recovering oil and solvent from that sub- 1| 5 sans applied herein to the fraction having the lower temperature coenicient of viscosity, lower carbonhydrogen ratio, etc., and the term naphthenic" to the relatively non-paramnic" fraction. i. e. .the fraction having the higher temperature coeilicient of viscosity.y higher carbon-hydrogen ratio, etc.

It is to be understood that although my process is particularly designed for the dewaxing and fractionation of wax-bearing mineral lubricating oils, it may also be applied with suitable modifications to vegetable and animal oils containing waxes or other high melting point substances. l, Although my invention has been described in connection with a variety of specific embodiments thereof, it is to be understood that I am not limited thereby to any greater extent than thescope of the appended claims, I claim:

1. A process of dewaxing and iractionating a wax-bearing cil into fractions relatively parafilnic and naphthenic with respect to the original oil which comprises mixing the oil with a selective solvent adapted to assist the precipitation of wax at low temperatures, chilling the mixture to alow temperature to cause precipitation of substantial wax, removing said wax, and chilling the remainder of the mixture containing saidy solvent to a lower temperature to cause the mixture to separate into two liquid phases. separating said phases and recovering the solvent therefrom.

2. A process of dewaxing and fractionating a wax-bearing lubricating oil comprising dissolving it in a selective solvent adapted to precipitate therefrom a maior portion of the wax contained therein. chilling to precipitate said wax, removing said precipitated wax, chilling the oil solution thus produced to a lower temperature than that used to precipitate the wax, said lower temperature being adapted to 'induce the formation of two liquid phases in said oil solution. separating the said two liquid phases from each other, each of said liquid phases containing a portion of the oil and a portion of the solvent, separately recovering oil and solvent from one of said two liquid phases, and recycling at least asubstantial portion of the other of said two liquid phases back to a point in the process prior to the wax removal step.

3. A process according to claim 2 in. which the 4oil solution passing from the wax 'removal' step is modified priol to further chilling to decrease its solvent power for relatively naphthenic oil fractions. 4

4. A process according to claim 2 in which the liquid phase recycled is that one of the two liquid phases which contains the greater proportion of solvent.

5. A processaccording to claim 2 in which the lliquidphaeerecycledis that oneofthetwoliquid phases which contains the more naphthenic oil.

- 6. Aprocess of dewaxing and fractionating a wax-bearing lubricating oil comprising dissolving it in a selective solvent adapted to precipitate therefromamaiorportionofthe waxcontained 654 therein, chilling to precipitate said maior portion of the wax contained therein. removing said precipitated wax. chilling the solution resulting from the removal of said precipitated wax to a lower temperature to produce twonsuhstentiall'y liquid 70 p stantially liquid phases containing a portion of l 'of a fresh portion of the solvent originally used to dissolve the wax-bearing lubricating oil.

8. A process according to claim 6 in whichthe composition of the solution passing from the wax removal step is modified .by the introduction thereinto of an additional solvent, said additional solvent being 'ultimately separately recovered from the products of the process. 9. A process for the dewaxing and fracionating of a wax-bearing mineral oil containing relatively paraflinic and relatively naphthenic constituents comprising dissolving said oil in a. se-

lective solvent, .chilling the solution thus formed to precipitate Wax therefrom, removing the precipitated wax, chilling the solution to a temperature lower than that at whichthe said wax was precipitated .to induce the formation of two substantially -liquid phasesfrom the said solution, each of said substantiallyv liquid phases being formed in substantial quantity, one of said subthe solvent and a relatively paraflinic portion of the oil, the other of said substantially liquid phases containing a portion of the solvent and a relatively naphthenic portion of the oil, separating said two substantially liquid phases from each other, distilling the phasev containing the more parainic oil to recover solvent therefrom, returning the solvent thus recovered -to the process,

chilling at least a portion of the phase containing the more naphthenic oil to a temperature lower than the temperature of any of the oil solutions at any previous stage of the process, to induce the formation of two additional substantially liquid phases -from the aforementioned phase vtion of the solvent and ahighly naphthenic portion of the oil and the other of said two substantially liquid phases containing a portion of the solvent and a portion of the oil intermediate in properties between the relatively paramnic and highly naphthenic portions previously mentioned, separating said two additional phases from each other, returning at least a part of one of the two phases last aforementioned to a previous stage of the process, separately recovering oil and solvent from the other of said phases, and returning the solvent thus recovered to a previous stage of the process.

l0. A process according to claim 9 in which the solution is modified at at least one point between the various phase removal steps to promote phase separation in the next successive step. v

1l. A process of dewaxing and fractionating a wax-bearing oil comprising dissolving said oil in a selective solvent adapted to precipitate therefrom at least a substantial portion of the wax contained therein, precipitating said wax, removing said wax, chilling the dewaxed solution to cause the formation of two phases therefrom, each of 'said phases containing a portion of the oil anda portion of the solvent, separating said two phases, recovering solvent from one of said two phases and from a portion of the other of said two phases, and recycling the remainder of said last-mentioned phase to a point in the process prior to the dewaxingstep.

12. A process according to claim 11 in which the selective solvent comprises a substance selected from the group consisting of butyl formate, butyl acetate, amy] acetate and phenyl acetate.

13. A process of dewaxing. and fractionating a wax-bearing oil comprising dissolving said oil in. a selective solvent adaptedto precipitate therefrom atleast a substantial portion of the wax contained therein, precipitating said wax, removing said wax, decr-easingV the oil solvent power of and chilling the dewaxed solution to cause the formation of two phases therefrom, each of said phases containing a portion of the oil and a portion of the solvent, separating said two phases, recovering solvent from one of said two phases and from a portion of the other -of said two phases, and recycling theremainder of said last-mentioned phase to a point in the process prior to the dewaxing step.

14. Process for the solvent fractionation of oils comprising the solvent fractionation of an oil into twophasea one of'said phases containing a relatively parainic portion of the oil and a portion Y of the solvent, theother of said phases containing a relatively naphthenic portionv of the oil and a portion of the solvent, chilling the last mentioned' of said phases to cause the formation of two further phases therefrom, one of said two further phases containing a highly naphthenic portion of the oil and a portion of the solvent, the other of said two further phases containing a portion of the solvent and a portion of the oil intermediate `in properties between said naphthenic portion and said highly naphthenic portion, separating vfrom at least a substantial portion of the wax contained therein, precipitating said wax, re-

moving said wax, chilling the dewaxed solution to cause the formation of two phases therefrom, separating said phases, further chilling at least a. substantial portion of one of said phases to said twofurther phases, and recycling at least a cause the formation o'f two further phases therefrom and recycling at least a substantial portion of one of said last-mentioned phases to a point y in the process priorto the dewaxing step.

16. A process according to claim 15 in which the selective solvent comprises nitrobenzene.

'I 17. A process for dewaxing and fractionating of Wax-bearing mineral oil containing relatively paraflinic and relatively naphthenic constituents,

comprising dissolving said oil in a selective solvent,.chilling the solution thus formed to a temperature adapted to precipitate wax therefrom,

removing the precipitated wax, adding to the dewaxed solution a substantial amount of a secondv second selective solvent from each of said phases.

' 18. A process for dewaxing a wax-bearing mineral' oil at a low temperature and then fractionating said mineral oil at a lower temperature which comprises dissolving said wax-bearing mineral oil in a solvent adapted'to' precipitate wax from said wax-bearing mineral oil at said* low temperature, chilling to said low temperature to precipitate said wax, removing the precipitated wax, adding a relatively poor oil solvent to' the solution to-decrease the solvent power of said solution for a portion oi the oil to the extent that a second liquid phase wouldy precipitate from said solution at said low temperature, chilling to said lower temperature to precipitate an amount of a second liquid phase'in excess of the amount which would precipitate at said low temperature and separating the two liquid phases formed at said lower temperature from each other.

19. In a combined process for-separating a wax bearing oil into wax and fractions respectively parainic and naphthenic with respect to the original oil, the steps which include dissolving the oil in a solvent which at 'a given temperature is selective between normally solid hydrocarbon constituents and normally liquid hydrocarbon constituentslof the wax bearing oil and which at somewhat lower temperatures is selective between paraflinic and naphthenic constituents of the oil,

which solvent also at the dewaxing temperature has a substantially minimum solvent power for wax, consistentwiththe retention of substantiallyall of the oil in solution, chilling the solution thus formed to a dewaxing temperature at which substantially all of the,wax' is insoluble, removing the wax while maintaining approximately said temperature, reducing the temperature'of the remaining solution below the dewaxing temperature, and' sufiiciently low to cause a separation of said remaining solution into two liquid phases, oneof said phases containing a relatively large-proportion of the solvent and a relatively naphthenic fraction of the oil, and the other of said phases containing a relatively small proportion oi the solvent and a relatively parafnic fraction of the oil, separating said two phases and separating the solvent from each of said phases.

20. In a combined processfor separating a wax bearing oil into wax and fractions respectively paralnic and naphthenic with respect to the original oil, the steps which include dissolving the oil in a solvent which at a given temperature is selective between normally' solid hydrocarbon constituents and normallyv liquid. hydrocarbon constituents of the wax bearing oil and which at temperatures approximately F. to 60 F. lower than said given temperature is selective between 'paraiinic and naphthenic constituents of the oil,

which solvent at said given temperatures has a substantially minimum solvent power for wax, consistent with the retention oi' substantially all ofthe oil in solution, chilling the solution thus formed to said given temperature to precipitate wax, removing the precipitated wax substantially at said .given temperature, reducing the temperature of the remaining solution to a point from about15 F. to about 60 F. lower than said given temperature to cause a separation of said oil into two liquid phases, one of said phases containing a relatively large proportion of the solvent and a relatively naphthenic fraction of the oil, and the l other of said phases containing a relatively small proportion of thesolvent and a relatively parafinic fraction of the oil, separating said two phases and separating the solvent from each of said phases.

21. The process of fractionating a lubricating oil into fractions which are respectively relatively parainic and relatively naphthenic with respect tothe original oil, which comprises mixing the oil with a selective solvent, chilling the mixture to a suiliciently low temperature to cause, the separation thereof into two phases, removing one phase from the other phase, further chilling one of said phases to eilect a further phase separation into a fraction consisting chiefly of oil and a fraction consistingchieily of solvent, and returning the fraction consisting chiefly of solvent to the system at a point prior to the first phase separation step.

GEORGE L, PARKHURST. 

